but I can't, because I'm in a wrong country. I would like to change country. Do I need to travel to another country to install this application or can I somehow pick a right country ? what is the right country for this application?

For the second part of your question about which country to change to, from the app's description:

Currently for U.S. and Canada based phones only.

But from this description:

The application dials to our service, which dials to the other party,
showing your phone number as the caller ID.

The service then records
the call at the telephony level, and sends a very high-quality
recording straight to your email box.

I think that even if you get it to install, it will only work properly if you are currently in the US or Canada, as it seems to work by redirecting your call through a landline call forwarding service, which either won't work in other countries, or will be using a hideously expensive international rate call for that purpose.

I had the same problem and asked Google to help me.
This is their answer:

We use the billing address of your default payment instrument in Google Wallet to help determine your home country for accessing the Play Store. Our collection of content can vary by country, so your view of the Play Store may differ from what others are seeing when you travel outside of the country listed on your default payment method's billing address.

Please note that you must have a valid payment method with a billing address located inside a country in order to access that country's Play Store.

If you're having issues viewing your intended country's Play Store and would like to change your default payment method or update an existing billing address in Google Wallet, please use the following steps:

2) Add a new card or change your default payment instrument to one with a billing address located inside your desired country

3) Open the Play Store and navigate to any item available for download

4) Click to begin a download until you reach the "Accept and buy" screen (no need to complete the purchase)

5) Close the Play Store and clear data for the Google Play Store application (Settings > Apps > Google Play Store > Clear Data) or clear your browser cache

6) Re-open the Play Store. You should now see the Play Store that matches your default payment instrument's billing country.

If you haven't yet added a payment method to your account for the first time, please add a card directly from the Play Store with a billing address that matches your intended country location. Then, follow steps 3 through 6 to show your intended country's Play Store.